Co3O4@PEI/Ti3C2Tx MXene nanocomposites for a highly sensitive NOx gas sensor with a low detection limit

A simple noncovalent chemical approach and hydrothermal method were used for effectively riveting Co3O4 nanocrystals to branched polyethylenimine (PEI) functionalized Ti3C2Tx MXene sheets to fabricate Co3O4@PEI/Ti3C2Tx MXene composites. Co3O4 nanoparticles as active center components were uniformly dispersed on Ti3C2Tx MXene with high specific surface area and abundant functional groups to form a heterogeneous structure. PEI, as a channel for electron transfer, effectively improved the interaction between Ti3C2Tx MXene and Co3O4. The diffusion capacity of NOx molecules and the electron transmission efficiency at the interface between adsorbed molecules and the surface of the material were improved, which contributed to the sensing performance of the material. Meanwhile, the highest sensing response to NOx gas was seen in the Co3O4@PEI/Ti3C2Tx MXene composites with 2.4 mg addition of Ti3C2Tx sheets (CoPM-24). CoPM-24 exhibited a response and response time of 27.9 and below 2 s for NOx gas at room temperature under humidity of 26%. Moreover, CoPM-24 also showed excellent selectivity, repeatability and a low experimental detection limit (30 ppb) for NOx gas. Thus, the Co3O4@PEI/Ti3C2Tx composites are potential high-sensitivity NOx gas sensor candidates.